Please note, this is not a part that customers commonly need to replace. In order to reduce any risk of damage to this part in future, please take note of the following:1) When the O-rings/piston are in good condition and are sealing properly, this should prevent chemicals leaking down to the black loosening ring. The piston O-rings (and the piston itself) should be regularly checked and replaced as required.2) You should also be careful not to apply lots of force to the piston to remove it, as this could damage the piston / loosening ring.